If you are doing a blend on base/clear, you should clear the entire panel that the repair was done on.
So if the repair is on the front of a fender, you will be blending the base from the repair area into the undamaged area. Then you will be clearing the entire fender.
You need about 18ish inched to do a proper and invisible blend so if the repair area is say..... towards the rear of the fender, about 10" from the door, you will be prepping, blending and clearing the entire fender and door.
Now sometimes it really isn't practical to carry your clear to a panel edge, for example:
If you were doing a blend in the rear quarter of something like a Dart, where is the panel edge that you would stop at?
Hint, it's on the other side of the car. To correctly blend the rear quarter on something like a 70 Dart, you would need to clear both rear quarters and up over the roof.
Not that most people would do that.....
You need to remember that the clear provides UV protection not only to the base but to itself. So if you blend out your clear within a panel and polish, that polished, clear edge is thin and will fail in a few years depending on it's exposure to sunlight.
#1 rule in blending....... Always run your clear to where the sun don't shine.
